The present invention relates to an inkjet recording apparatus, and in particular, to an inkjet recording apparatus in which a feeding accuracy of a recording medium in a sub-scanning direction is improved.
In an inkjet recording apparatus for recording desired images by ejecting ink droplets on the recording medium, the recording head for ejecting the ink droplets is moved above the recording medium in the main scanning direction, and thereafter the recording head, with respect to each line recording, is repeatedly moved, in the sub-scanning direction, which is perpendicular to the main scanning direction.
Heretofore, the movement of the recording medium in the sub-scanning direction was generally achieved by the intermittent feeding operation of a stepping motor, or by a DC motor having a rotary encoder. In the former case, when one line is recorded by the recording head in the main scanning direction, the predetermined number of pulses is applied to the stepping motor, and this number of pulses becomes the feeding distance, which is the predetermined length (patent document 1) to feed the recording medium in the sub feeding direction. While in the latter case, feeding of the recording medium in the sub-scanning direction is read from the counted number of pulses generated by the rotary encoder, and thereby the movement of the recording medium is controlled by the counted number of pulses by which the predetermined feeding amount can be obtained. (patent document 2).
Further, there is a case wherein the rotary encoder is installed on a rotating shaft of a feeding roller which feeds the recording medium in the sub-scanning direction, and therefore the feeding amount is controlled by the counted number of pulses (patent document 3).                [patent document 1] Tokkaihei 11-334160        [patent document 2] Tokkaisyou 59-171664        [patent document 3] Tokkaihei 4-19149        
In recent years, in order to record the images with extended definition at a high speed, the number of the nozzles of the recording head was increased, as was the length of the nozzle array of the recording head, and since the length of the recording head in the sub-scanning direction increased, it essentially required the improvement of the feeding accuracy. For example, recently researched was an image recording method to obtain extended definition images having no banding, by printing the images by each block. Such a recording method requires a greater feeding distance of the recording medium in the sub-scanning direction at one time, therefore, a dramatic increase of feeding accuracy is essential, which however has not been used practically.
Because, the feeding amount of the recording medium on the inkjet recording apparatus is indirectly affected by only counting the pulses of the stepping motor to drive a feeding roller of the recording medium, or the pulses generated by the rotary encoder, and thereby errors occur in the practice in the fed amount of recording medium, which in turn causes a white band between each block of printing, deteriorating the image quality.
That is, whichever device may be used the stepping motor or the DC servo motor integrated with the rotary encoder, the feeding amount of the recording medium which is obtained by the counted number of pulses, does not show the real fed amount, owing to factors such as errors of diameter of the feeding roller and the shaft center position of the feeding roller, the difference between the thickness of the recording media, and the slip generated between the feeding roller and the recording medium, resulting in errors of the real fed amount of the recording medium, and thereby generating white bands. Such a problem may be solved by installing the rotary encoder on the rotating shaft of the feeding roller, this however does not obtain sufficient improvement when the feeding distance increases.